1. Technical Field
The present invention relates to a drive system abnormality detecting apparatus of an injection-molding machine for detecting an abnormal situation of resin pressure detecting means or screw drive means for axially driving a screw of the injection-molding machine.
2. Background Art
In order to make a resin pressure, e.g., the resin pressure inside a cylinder equal to a set resin pressure, in an injection-molding machine, the resin pressure inside the cylinder is indirectly measured by means of resin pressure detecting means which is disposed at the rear end of a screw. The measured resin pressure is compared with a screw injection pressure set by means of injection pressure setting means. If the resin pressure inside the cylinder is lower than the set screw injection pressure, the screw is driven in the direction to raise the resin pressure inside the cylinder. If the the resin pressure inside the cylinder is higher than the set screw injection pressure, on the other hand, the screw is driven in the direction to lower the resin pressure inside the cylinder. Thus, closed loop drive control is effected.
According to the prior art described above, proper closed-loop control can be accomplished if both the resin pressure detecting means and the screw drive means are in the normal state. If either the resin pressure detecting means of the screw drive means malfunctions, however, proper closed-loop control cannot be achieved.
If the resin pressure detecting means becomes out of order, thus becoming unable to measure the resin pressure inside the cylinder, for example, it is impossible to keep the resin pressure inside the cylinder at the set resin pressure, and the repetition accuracy of pressure control for the molding operation is considerably lowered, thereby inducing the occurrence of defective molding. Moreover, if the screw drive means (hereinafter referred to as injection drive means) for axially driving the screw is compulsorily driven in the direction to raise the resin pressure inside the cylinder, on the basis of a measured value given by the resin pressure detecting means in trouble, the injection drive means is subjected to overload, so that the screw, drive system, dies, etc. are adversely affected. In addition, the resin pressure inside the cylinder increases extraordinarily, thereby creating a very dangerous situation.
In case of trouble in the injection drive means, moreover, the drive means cannot properly respond to feedback input despite the normality thereof. Thus, the same problems as aforesaid are caused.